This invention relates to snapshot differential copying in a storage system.
Background art in the technical field of this invention includes WO 2012/164618 A1. In Abstract of WO 2012/164618 A1, there is described that “A storage system is provided with a memory region, a cache memory region, and a processor. The memory region stores time relation information that indicates a time relationship of a data element that has been stored into the cache memory region and that is to be written to the logical region and a snapshot acquisition point of time to the primary volume. The processor judges whether or not the data element that has been stored into the cache memory region is a snapshot configuration element based on the time relation information for the data element that is to be written to a logical region of a write destination that conforms to the write request that specifies the primary volume and that has been stored into the cache memory region. In the case in which the result of the judgment is positive, the processor saves the data element to the secondary volume for holding a snapshot image in which the snapshot configuration element is a configuration element, and a data element of a write target is then stored into the cache memory region”.